<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container{
            display:flex;
        }
        .left{
            width:180px;
            border:1px solid red;
        }
        .right{
            flex:1;

            border:1px solid blue;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="left">我是侧边栏</div>
        <div class="right">
            我是外部内容水水水水
        </div>
    </div>
</body>
</html>